The South African Republic (Dutch: Zuid-Afrikaansche Republiek, abbreviated ZAR; Afrikaans: Suid-Afrikaanse Republiek), also known as the Transvaal Republic, was an independent Boer republic in Southern Africa which existed from 1852 to 1902, when it was annexed into the British Empire as a result of the Second Boer War.

The ZAR was established as a result of the 1852 Sand River Convention, in which the British government agreed to formally recognise independence of the Boers living north of the Vaal River. Relations between the ZAR and Britain started to deteriorate after the British Cape Colony expanded into the Southern African interior, eventually leading to the outbreak of the First Boer War between the two nations. The Boer victory confirmed the ZAR's independence; however, Anglo-ZAR tensions soon flared up again over various diplomatic issues. In 1899, war again broke out between Britain and the ZAR, which was swiftly occupied by the British military. Many Boer combatants in the ZAR refused to surrender, leading British commander Lord Kitchener to order the adoption of several scorched-earth policies. In the treaty which ended the war, the ZAR was transformed into the Transvaal Colony, and eventually the Union of South Africa. During World War I, there was a failed attempt at resurrecting the republic in the Maritz rebellion.

The land area that was once the ZAR now comprises all or most of the provinces of Gauteng, Limpopo, Mpumalanga, and North West in the northeastern portion of the modern-day Republic of South Africa.